The existing clamping structure for a handled tool, e.g., drill chuck, generally consists of body, jaws, nut, bearing, anti-loose device and outer sleeve, wherein the body is connected to the driving spindle of the power device, the three jaws are mounted respectively in the three guiding grooves spaced equally on the body and provided with threads to form screw drive with the nut. Rotating the outer sleeve connected with the nut will cause the jaws to move in the guiding grooves relative to the body, resulting in that the tool handle is clamped or released.
For the above structure, the thread between the jaws and the nut produces very large contact stress under working load, which leading the friction of the relative slide being large. Consequently, the clamping force for clamping the tool handle, produced by the screw drive between the nut and the jaws, is difficult to be large enough. Such that the tool handle can not be clamped tightly by the jaws under the operating condition of heavy load and vibration. Additionally, for those published anti-loose structures, the anti-loose effects are not good enough because of the structure limitation. For instance, in PCT/CN02/00375, there is a hidden-trouble of looseness in the structure under the operating condition of vibration and impact.
It has been known that some clamping structures adopted the one-way clutch in order to improve the performance of the locking engagement and prevent the release of the jaws during the operation process.
U.S. Pat. No. 5,031,925 disclosed a clamping structure for rotary tool with one-way clutch. FIG. 47 is a longitudinal partial-sectional front view of the clamping structure in prior art, and FIG. 48 is a cross sectional view of the clamping structure taken along position I-I in FIG. 47. As shown in FIGS. 47 and 48, the clamping structure comprises chuck body 1′, rear cap 2′, three pawls 3′, a control outer sleeve 4′, a pawl seat 5′, a pawl 6′, and a control member 7′, wherein the chuck body 1′ has longitudinal central axis and connects at its rear end to a driving shaft of a driving apparatus for driving the chuck body 1′ to rotate about the central axis. The rear cap 2′ is provided fixedly at the rear end of the chuck body 1′ and has longitudinal strias on its circumference forming a grasping portion. The control outer sleeve 4′ is mounted rotatablely around the exterior of the chuck body 1′ and locates at the front of the rear cap 2′, the outer surface thereof forming with a second grasping portion. The control outer sleeve 4′ is connected at its inner side to the control member 7′ and drives it. The control member 7′ depresses the rear end of the pawl member 6′ to disengage the pawl 6′ a at the front end from the ratchets provided at the chuck body 1′.
The pawl member of the clamping structure engages the ratchets with its pawl portion in the state of operation. When the tool handle being clamped is to be released, it is required to disengage completely the pawl portion from the ratchets. However, in the current clamping structure, the mechanism that disengage the pawl portion of the pawl member from the ratchets is not reliable such that a half-disengagement state is often caused, therefore when releasing or re-clamping the tool handle, the pawl and the ratchets scrapes from each other, resulting in the phenomenon of teeth scraping, which lessens the performance of the clamping structure.